undo 310c2a3 ('change default log level to info') - fixes S::S

In 310c2a39c the Catalyst::Log conststructor was modified to strip
'debug' from the list of of levels by replacing a call to the keys of
%LEVELS with a hard-coded list. This broke the test suite of
Static::Simple and has been rolled back for now. With this change, now
the S::S tests should pass, and, hopefully the whole travis test suite,
including the new resverse dep testing...

The original intent to 'change the default log level from debug to info'
now needs to be revisited...

Commands used for reference:

 git checkout 5.90065 -- lib/Catalyst/Log.pm
 git checkout 5.90065 -- t/aggregate/unit_core_setup.t
 git checkout 5.90065 -- t/aggregate/unit_core_setup_log.t

Other files changed in 310c2a39c but *not* reverted in this commit:

 Changes
 t/lib/TestApp/Controller/Log.pm
 t/psgi-log.t